Pixel art for web and UI applications is a specialized area with its own rules that differ from game-oriented pixel art. I've done both and want to note the key differences.

Game pixel art is designed to be viewed at specific scales, in motion, against specific backgrounds. The palette and level of detail are calibrated for the game engine's rendering context.

Web and UI pixel art needs to work at variable display densities and may be viewed on screens that aren't calibrated to show pixel art without anti-aliasing. This changes the design approach: you need pixels that are large enough to read clearly when accidentally anti-aliased, or you need to export at multiple resolutions with crisp scaling.

Icon pixel art specifically: the 16x16 and 32x32 constraints require complete legibility at tiny sizes. Every pixel carries information. The silhouette must communicate the icon's meaning at thumbnail size with no text support.